Thermal printing head

ABSTRACT

A thermal printing head comprising a plurality of thin insulating layers each being provided on one surface thereof with a plurality of lower slips made of an electrically conductive material arranged in spaced parallel relation to one another. The insulating layers are piled stepwise one upon another so that one end portion of the upper surface of each of the layers with the corresponding end portions of the conductive slips thereon are exposed from beneath the end of the layer immediately above. A square element made of an electrically resistive material is placed on each of the exposed end portions of the lower conductive slips. An upper slip made of an electrically conductive material extending transversely of the exposed ends of the lower conductive slips on each of the insulating layers covers the resistive elements so that the elements are sandwiched between the upper and lower conductive slips. Upon impression of a voltage between the upper and lower conductive slips, the resistive elements sandwiched therebetween are heated. By selecting the lower conductive slips between which and the upper conductive slip a voltage is to be impressed it is possible to heat those of the resistive elements which are combined to take the shape of a symbol, and with a sheet of heat-sensitive paper being applied onto the surface of the printing head, the symbol is printed on the paper.

United States Patent [1 1 Taniguchi 1 Sept. 3, 1974 THERMAL PRINTING HEAD [75] Inventor: Hideo Tanlguchi, Kyoto, Japan [73] Assignee: Toyo Electronics Industry Corp.,

Ukyo-ku, Kyoto, Japan [22] Filed: Mar. 8, 1973 [21] Appl. No.: 339,432

[30] Foreign Application Priority Data Mar. 16, 1972 Japan 47-4726795 [52] US. Cl. 219/216, 219/543 [51] Int. Cl. H05b 1/00 [58] Field of Search 219/216, 543; 346/76 [56] References Cited UNITED STATES PATENTS 3,483,356 12/1969 Kalt 346/76 X Primary Examiner-C. L. Albritton Attorney, Agent, or Firm-Christensen, OConnor, Garrison & Havelka [5 7] ABSTRACT A thermal printing head comprising a plurality of thin insulating layers eachbeing provided on one surface 254 /6/l/56 252% a; w w an M- thereof with a plurality of lower slips made of an electrically conductive material arranged in spaced parallel relation to one another. The insulating layers are piled stepwise one upon another so that one end portion of the upper surface of each of the layers with the corresponding end portions of the conductive slips thereon are exposed from beneath the end of the layer immediately above. A square element made of an electrically resistive material is placed on each of the exposed end portions of the lower conductive slips. An upper slip made of an electrically conductive material extending transversely of the exposed ends of the lower conductive slips on each of the insulating layers covers the resistive elements so that the elements are sandwiched between the upper and lower conductive slips. Upon impression of a voltage between the upper and lower conductive slips, the resistive elements sandwiched therebetween are heated. By selecting the lower conductive slips between which and the upper conductive slip a voltage is to be impressed it is possible to heat those of the resistive elements which are combined to take the shape of a symbol, and with a sheet of heat-sensitive paper being applied onto the surface of the printing head, the symbol is printed on the paper.

18 Claims, 7 Drawing Figures THERMAL PRINTING HEAD This invention relates to a rprinting head for use in thermal printing.

Recently there have been in wide use thermal printers which employ a thermal printing head to record information obtained from, say, an electronic computer in the form of various symbols printed on heat-sensitive recording media. The thermal printing head includes those elements which produce heat when electric energy is applied thereto. For printing, the elements are selectively heated to form a required symbol to be pressed onto the heat-sensitive paper so that the symbol is recorded on the paper. It is required of such a printing head that a single head should be capable of selectively printing a plurality of different symbols (including characters, pictures, etc).

In one known printing head, there are provided many dot-like heating elements arranged in rows and columns and spaced equidistantly from one another. When a symbol is to be printed by the printing head, those of the elements which correspond to the symbol are selectively energized to be heated, so that the heated elements are combined to form the shape of the symbol. Therefore, when the head is brought into contact with a sheet of heat-sensitive paper, those dotlike portions of the paper which are contacted by the heated elements become colored, and the colored dots are combined to appear as the required symbol.

One prior art printing head having such dot-like heating elements comprises a plurality of thin layers of an insulating material laminated into a single block each layer being provided on one side surface thereof with a plurality of separate thin heating elements, so that on the side or surface of the block there appear a plurality of dot-like heating elements arranged in rows and columns and spaced a predetermined distance apart from one another. For supply of electric energy to each of the elements, on one surface of the insulating layer there is provided a thin layer of an electrically conductive material, through which electric current is supplied to the heating element.

For manufacture of the printing head of the abovementioned type, it is necessary to provide dot-like heating elements on one side surface of each insulating layer, and these heating elements are film resistors formed on the surface by chemical deposition. The manufacturing process is rather complicated and timeconsuming and requires a high degree of skill and precision.

Accordingly, the primary object of the invention is to provide a thermal printing head which is provided with a plurality of dot-like heating resistive elements.

Another object of the invention is to provide such a thermal printing head as aforesaid in which the heating resistive elements and the electrically conductive elements for supplying electric energy to the resistive elements are composed of a thick film.

Still another object of the invention is to provide such a thermal printing head as aforesaid wherein the terminals through which electric energy is supplied to the resistive elements are arranged in a substantial plane.

The thermal printing head of the invention comprises a plurality of thin layers of an electrically insulating material each being provided on one surface thereof with a plurality of slips of an electrically conductive material arranged on the surface in spaced parallel relation to each other. These insulating layers are piled stepwise one upon another into a unitary structure. The word stepwise means that the layers are so piled one upon another that one end portion of the upper surface of each layer with the corresponding end portions of the conductive slips thereon is exposed from beneath the corresponding end of the layer immediately above as if those exposed end portions of the layers formed stairs. A square patch or element of an electrically resistive material is placed on the end portions of the conductive slips on the exposed end portion of each of the insulating layers. A slip of an electrically conductive material extending transversely of the exposed ends of the conductive slips on each of the insulating layers is placed in contact with all the square resistive elements so as to electrically connect the elements. In the following description those conductive slips which are directly placed on the insulating layer will be referred to as the lower conductive slips and that which is placed on the resistive elements, as the upper conductive slip.

If one of the lower conductive slips on one of the insulating layers is selected and a voltage is impressed between the selected lower conductive slip and the upper conductive slip, an electric current flows through the resistive element sandwiched between the upper and lower slips in the direction of the thickness of the elements so that the element is heated. The heat is transferred to that local portion of the upper conductive slip which corresponds to the resistive element.

If more than one of the lower conductive slips on each insulating layer is selected so as to impress a voltage between the selected slips and the common upper conductive slip, the corresponding local areas of the upper slips are heated. The heated areas are separate and dot-like, but when all the heated dot-like areas on the exposed surface of all the insulating layers are taken as a whole, they express a symbol or character. Therefore, if a sheet of heat-sensitive paper is applied onto the surface of the printing head, the symbol appears or is printed on the paper.

As previously mentioned, the insulating layers are piled stepwise. However, since each of the layers, the slips and the resistive elements is as thin as 0.015 mm, the upper surface of the printing head is practically flat. However, if the stepped surface causes any trouble to clear printing, projections of a thermally conductive material may be provided on those portions or areas of the upper conductive slip which correspond to the resistive elements below the slip. The projections are of such a height that their upper surfaces are in substantially the same plane. With this arrangement, the surfaces of all the projections can be applied to a sheet of heat-sensitive paper with substantially the same pressure so that a clear printing is obtained.

The insulating layers are piled stepwise also at the side opposite to that where the resistive elements are provided so that the corresponding ends of the lower conductive slips on the insulating layers are exposed at that side, which can be used as terminals through which electric energy can be applied to the slips. With this arrangement there is no need for provision of particular terminals or leads for the purpose.

On each of the insulating layers there is further provided an additional electrically conductive slip extending alongside the lower condsuctive slips. This additional slip may be referred'to as the common conductive slip. The slip has its one end electrically connected to the upper conductive slip on that insulating layer'and its opposite end exposed at the opposite exposed end of the insulating layer in the same manner as the exposed terminal ends of the lower conductive slips. The exposed end of the common conductive slip can advantageously be used as the terminal of the upper conductive slip on that insulating layer. The invention will be described further in detail with reference to the accompanying drawings, wherein:

FIG. 1 is a top plan view of one form of the thermal printing head of the invention, with its middle portion being eliminated for ease of illustration;

FIG. 2 is a schematic enlarged perspective view of a portion of FIG. 1;

FIGS. 3 5 are perspective views similar to FIG. 2 but showing different embodiments;

FIG. 6 is an enlarged side view, in vertical section, of a projection formed on the heat-producing portion of the printing surface of the head; and

FIG. 7 is a view similar to FIG. 6 but showing a moditied form of the projection.

Referring in detail to the drawings, there'is shown a printing head comprising a plurality, say, seven, layers 1A 1G made of a suitable insulating material such as alumina or the like ceramic piled one upon another. The layers 1A 1G are supported by a base 10 made of a suitable material. The base and the layers thereon form a unitary structure. If the base is made of an insulating material, the lowest layer 1A may be eliminated.

On the upper surface of the lowest layer 1A there are provided a plurality, say, six slips 1 1A 16A of an electrically conductive material arranged in parallel with and equidistantly spaced from one another. In a similar manner, there are provided on the surface of each of the insulating layers 1B 1G six parallel conductive slips 11B 16B, 11C 16C, 11D 16D,'11E 16E, 11F 16F and 11G 16G. Of these conductive slips the slips 16A 16G are the common conductive slips while the rest are the lower conductive slips. The insulating layers are piled stepwise one upon another so that the one end portions of the conductive slips are exposed and the exposed areas of the insulating layers appear as if they formed stairs.

A square patch or element 21A 25A made of an electrically resistive material is placed on each of the exposed end portions of the lower conductive slips 1A 16A on the lowest insulating layer 1A. In a similar manner, resistive elements 21B 25B, 21C 25C, 21D 25D, 21E 25E, 21F 25F and 21G 25G are provided on the-exposed end portions of the lower conductive slips on the other insulating layers 1B 10.

An upper conductive slip 3A extending transversely of the exposed ends of the lower conductive slips 11A 14 15A on the lowest insulating layer 1A is placed on the resistive elements 21A 25A in electrical contact therewith. The slip 3A has its one'end'also placed on the common conductive slip 16A so as to provide an electrical connection between the two slips 3A and 16A. In a similar'm'anner upper conductive slips 3B 3G are provided'on the other insulating layers 1B 1G and electrically connected to thecommon conductive slips 16B 166. These slips andelements are formed by the method of screen printing. Although in the drawing there appears a gap between, the under surface of the upper conductive layer and the upper surface of the insulating layer, this is merely for ease of illustration and actually there no such gap between the two surfaces.

The end portions of the insulating layers opposite to those portions where the resistive elements and the upper conductive slips are provided are also arranged stepwise so that the corresponding end portions of the lower and common conductive slips are exposed so as to be used as terminals and leads through which electric energy is applied to the slips.

As the material for the insulating layers a ceramic such as alumina is used. On a sheet of alumina there are provided a plurality of lower and common conductive slips which are formed by the method of screen printing. A plurality of such sheets are piled one upon another stepwise at the opposite end portions thereof and sintered to form a unitary structure. At the stepped end portion of the structure there are formed by the method of screeen printing a plurality of resistive elements on the exposed end portions of the lower conductive slips and then an upper conductive slip on the resistive elements.

In one printing head manufactured in the abovementioned manner, the width of the conductive slips and the resistive elements, and the gap between adjacent two of the conductive slips are all about 0.2 mm, the thickness of each of the conductive slips and the resistive element is about 0.015 mm, and the distance between the edge of each of the insulating layers and the upper conductive slip thereon is about 0.1 mm. With these dimensions, each of the resistive elements (which are heated) is a square one side of which is 0.2 mm

long, and these square elements exist as dots equidistantly spaced from one another on the upper surface of the printing head.

Suppose that a pulse-like voltage is impressed between, say, the lower conductive slip 11A and the common conductive slip 3A so that the element is heated. The heat is transferred to that local portion of the upper conductive slip which coreesponds to the resistive element. As will be easily understood, by selecting the lower conductive slips between which a voltage is to be applied it is possible to heat those of the resistive elements which are combined to take the shape of a required symbol.

If in FIG. 1 those of the resistive elements which are hatched are heated, the heated elements 21A 25A, 25B, 24C, 23D, 24D, 25E, 21F, 25F, 22G and 24G as a whole take the shape of the reversed numeral 3. In order to heat these hatched portions, a voltagev is applied between the common slip 16A and each of the lower conductive slips 11A 15A; the common conductive slip 16B and the lower conductive slip 15B; the

common conductive slip 16C and the lowerconductive slip 14C; the common conductive slip 16D and each of the lower slips 13D and 14D, 16E and each of 11F and 15F; and 16G and each of 126, 13G and 14G. With the printing head being impressed onto a sheet of heatsens'itive paper, when these resistive elements are. heated in the above manner, the corresponding portions of the paper change its color so that the numeral 3" appears or is printed thereon. I

Application of a voltage to the conductive slips is made through those ends of the conductive slips which are opposite to the ends thereof where the resistive elements are provided, that is, through those ends of the lower conductive slips and the common conductive slip which are exposed on the stepped end portions of the insulating layers. Since the ends of all the conductive slips are exposed, they can be used as terminals through which a voltage can be applied to the slips with case.

In the above example, the resistive element is sandwiched between the upper and lower conductive slips at each of the intersections thereof. In FIG. 3 a single slip made of an electrically resistive material replaces the separate resistive elements on each of the insulating layers. In the drawing three of such resistive slips are shown at 2A 2C, extending transversely of and in contact with the exposed end portions of the lower conductive slips on each of the insulaing layers. The arrangement of FIG. 3 is easier to manufacture than that of FIG. 1 since a single resistive slip suffices in FIG. 3 instead of the many elements separately provided in FIG. 2.

In FIG. 2, the upper conductive slip makes a right angle with the lower conductive slips on one and the same insulating layer. In FIG. 4, however, an upper conductive slip 31A extends in the same direction as the lower conductive slips 11A 11G on all the insulating layers, so that the upper conductive slip 31A covers the resistive elements 21A 21G in electrical contact therewith. In a similar manner, upper conductive slips 32A 34A are provided to cover the resistive elements 22A 22G, 23A 23G and 24A 240, respectively.

An improved modification of the arrangement of FIG. 4 is shown in FIG. 5, wherein a single upper conductive sheet 3 replaces the separate upper conductive slips of FIG. 4 and covers all the resistive elements on the insulating layers. With this arrangement it is possible to use the upper conductive sheet in common with any of the lower conductive slips, and the manufacture of this structure is much easier.

As will be easily understood, an electric current flows through the resistive element in the direction of its thickness because the element is sandwiched between the upper and lower conductive slips. Therefore if the thickness of the resistive element is uniform all over its area, the density of electric current per unit area of the resistive element is uniform all over its area so that the amount of heat produced per unit area of the element is uniform. However, if a pair'of conductive members were connected to the opposite sides of the resistive leement, the current would flow in the direction perpendicular to the direction of the thickness of the element. In this case, if the length of the heated portion of the element changes, the voltage to be applied must accordingly be changed. In this invention, however, even if the heated area of the resistive element changes, the voltage to be applied need not be changed and the density of electric current per unit area remains unchanged, so that uniformity in heating can be effected more easily than otherwise.

In the above described embodiments, since the insulating layers are piled stepwise, strictly speaking the upper surfaces of the conductive slips are at different levels above the upper surface of the base 10. In other words, the printing surface of the head is not strictly flat or plane but rugged. The insulating layers are so thin that the above-mentioned difference in level may be small. However, when the printingsurface of the head is applied onto a sheet of thermally sensitive paper, the contacting pressure may differ at different parts of the contacting surface of the head, with resulting unevenness or obscruity in the print obtained.

To solve the problem, a projection made of a thermally conductive material may be provided on those portions of the upper conductive slip on each of the insulating layers to which heat is transferred from the resistive elements beneath the slip, that is, those portions of the upper conductive slip which overlap the exposed end portions of the lower conductive slips on each of the insulating layers. The upper surfaces of the projections on different insulating layers are at substantially the same level above the upper surface of the base 10.

In FIG. 6 the whole upper surface of the printing head except for those portions at which the abovementioned projections are to be provided is first covered by an insulating layer 41 by the method of screen printing, and then a metallic bump 42 is fixed in each of the portions on which there is no overlying insulating layer 41.

In FIG. 7 a projection 43 is formed without initially forming no such overlying insulating layer as 41 in FIG. 6. The projection 43 comprises three layers 44 of a metallic material screen-printed three times on the upper conductive slip 3A. As previously mentioned, all the bumps 42 or projections 43 are so formed that their upper surfaces are at the same level.

In the illustrated embodiments, the printing head is designed so as to print a single symbol or character. In order to print a plurality of symbols at one time, a plurality of matrices each comprising any one of the illustrated constructions may be arranged side by side. In this case it is possible to use the insulating layers and the upper conductive slips or sheet in common with different matrices.

What I claim is:

l. A thermal printing head comprising: a plurality of layers of an electrically insulating material piled one upon another stepwise so that one end portion of one surface of each said layer is exposed from under the layer immediately above; a plurality of lower slips of an electrically conductive material arranged in parallel spaced relation to one another on said one surface of each said insulating layer; a plurality of elements of an electrically resistive material provided on the exposed end portions of said lower conductive slips on each said insulating layer; and an upper slip of an electrically conductive material provided on said resistive elements; whereby upon impression of a voltage between said upper and lower conductive slips an electric current flows through said resistive elements in the direction of the thickness thereof so as to heat said elements.

2. The thermal printing head of claim 1, wherein said resistive elements are arranged in rowsand columns equidistantly spaced from one another.

3. The thermal printing head of claim 1, wherein selected ones of said resistive elements can be energized to form a predetermined symbol.

4. The thermal printing head of claim 1, wherein said conductive slips and said resistive elements are formed by the method of screen printing.

5. The thermal printing head of claim 1, wherein said insulating layers are of a raw thin ceramic sheet sintered into a unitary structure.

6. The thermal printing head of claim 1, wherein said insulating layers are of a raw thin ceramic sheet having said conductive slips formed thereon by the method of screen printing before said layers are sintered.

7. The thermal printing head of claim 1, wherein said insulating layers are piled one upon another stepwise also at the other end portions thereof opposite to said end portions where said resistive elements are provided, so that the corresponding end portions of said lower conductive slips on each said insulating layer are exposed from beneath the insulating layer immediately above for use as terminals through which electric energy is applied to said conductive slips.

8. The thermal printing head of claim 1, wherein a voltage is impressed between said upper conductive slip and at least one of said lower conductive slips so as to heat those of said resistive elements sandwiched between said upper slip and said lower slips.

9. The thermal printing head of claim 1, further including an additional conductive slip electrically connected to said upper conductive slip on each said insulating layer to be used as a terminal for application of electric energy to said upper conductive slip.

10. The thermal printing head of claim 1, wherein said upper conductive slips extend in the same direction as said lower conductive slips so as to cover those of said resistive elements which are aligned in said direction on said insulating layers.

11. The thermal printing head of claim 1, wherein said upper conductive slips are formed into a single sheet.

12. The thermal printing head of claim 1, wherein a projection made of a thermally conductive material is formed on those portions of said upper conductive slip on each said insulating layer which correspond to said resistive elements beneath said slip, the upper end surfaces of said projections being arranged at substantially the same level.

13. The thermal printing head of claim 12, wherein said projections are formed by the method of screen printing.

14. The thermal printing head of claim 13, wherein said projections comprise a plurality of layers of a thermally conductive material.

15. The thermal printing head of claim 12, wherein each said projection comprises a bump of a thermally conductive material.

16. The thermal printing head of claim 1, wherein said resistive elements on each said insulating layer are formed into a single slip extending transversely of said lower conductive slips.

17. The thermal printing head of claim 1, wherein said upper conductive slips extend transversely of said lower conductive slips so as to contact those resistive elements associated with one insulating layer.

18. The thermal printing head of claim 1, wherein said upper conductive slips are arranged to contact said resistive elements such that each of the plurality of resistive elements is electrically common to one another. 

1. A thermal printing head comprising: a plurality of layers of an electrically insulating material piled one upon another stepwise so that one end portion of one surface of each said layer is exposed from under the layer immediately above; a plurality of lower slips of an electrically conductive material arranged in parallel spaced relation to one another on said one surface of each said insulating layer; a plurality of elements of an electrically resistive material provided on the exposed end portions of said lower conductive slips on each said insulating layer; and an upper slip of an electrically conductive material provided on said resistive elements; whereby upon impression of a voltage between said upper and lower conductive slips an electric current flows through said resistive elements in the direction of the thickness thereof so as to heat said elements.
 2. The thermal printing head of claim 1, wherein said resistive elements are arranged in rows and columns equidistantly spaced from one another.
 3. The thermal printing head of claim 1, wherein selected ones of said resistive elements can be energized to form a predetermined symbol.
 4. The thermal printing head of claim 1, wherein said conductive slips and said resistive elements are formed by the method of screen printing.
 5. The thermal printing head of claim 1, wherein said insulating layers are of a raw thin ceramic sheet sintered into a unitary structure.
 6. The thermal printing head of claim 1, wherein said insulating layers are of a raw thin ceramic sheet having said conductive slips formed thereon by the method of screen printing before said layers are sintered.
 7. The thermal printing head of claim 1, wherein said insulating layers are piled one upon another stepwise also at the other end portions thereof opposite to said end portions where said resistive elements are provided, so that the corresponding end portions of said lower conductive slips on each said insulating layer are exposed from beneath the insulating layer immediately above for use as terminals through which electric energy is applied to said conductive slips.
 8. The thermal printing head of claim 1, wherein a voltage is impressed between said upper conductive slip and at least one of said lower conductive slips so as to heat those of said resistive elements sandwiched between said upper slip and said lower slips.
 9. The thermal printing head of claim 1, further including an additional conductive slip electrically connected to said upper conductive slip on each said insulating layer to be used as a terminal for application of electric energy to said upper conductive slip.
 10. The thermal printing head of claim 1, wherein said upper conductive slips extend in the same direction as said lower conductive slips so as to cover those of said resistIve elements which are aligned in said direction on said insulating layers.
 11. The thermal printing head of claim 1, wherein said upper conductive slips are formed into a single sheet.
 12. The thermal printing head of claim 1, wherein a projection made of a thermally conductive material is formed on those portions of said upper conductive slip on each said insulating layer which correspond to said resistive elements beneath said slip, the upper end surfaces of said projections being arranged at substantially the same level.
 13. The thermal printing head of claim 12, wherein said projections are formed by the method of screen printing.
 14. The thermal printing head of claim 13, wherein said projections comprise a plurality of layers of a thermally conductive material.
 15. The thermal printing head of claim 12, wherein each said projection comprises a bump of a thermally conductive material.
 16. The thermal printing head of claim 1, wherein said resistive elements on each said insulating layer are formed into a single slip extending transversely of said lower conductive slips.
 17. The thermal printing head of claim 1, wherein said upper conductive slips extend transversely of said lower conductive slips so as to contact those resistive elements associated with one insulating layer.
 18. The thermal printing head of claim 1, wherein said upper conductive slips are arranged to contact said resistive elements such that each of the plurality of resistive elements is electrically common to one another. 